• Journal of the Korean Society for Marine Environment & Energy
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• v.7 no.4
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• pp.216-223
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• 2004

A nonlinear sloshing problem is numerically simulated. During excessive sloshing the sloshinginduced impact load can cause a critical damage on the tank structure. A three-dimensional free-surface flow in a tank is formulated in the scope of potential flow theory. The exact nonlinear free-surface condition is satisfied numerically. A finite-element method based on Hamiltons principle is employed as a numerical scheme. The problem is treated as an initial-value problem. The computations are made through an iterative method at each time step. The hydrodynamic loading on the pillar in the tank is computed.

• Polymer(Korea)
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• v.29 no.2
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• pp.151-155
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• 2005

The effect of acid-base treatments of carbon blacks (CBs) was investigated in the mechanical properties of CBs/rubber composites. The surface characteristics of the CBs were determined by the pH, acid-base values, and surface energetics. Their mechanical properties of the composites were also evaluated by the crosslink density $(V_e)$ and tearing energy (T). As an experimental result, acidically treated CBs led to the increase of the specific component $({\gamma}s^{sp})$, resulting in decreasing the mechanical properties of the composites. However, basically treated CBs showed a higher value of the dispersive component $({\gamma}s^L)$ than that of the untreated or acidically treated CBs. It was also found that the interaction of the CBs-rubber was improved, resulting in the improvement of the crosslink density and mechanical properties of the composites. It was then remarked that the acid-base characteristics of the CB surfaces made an important role in improving the physical properties of the rubber matrix composites.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.5
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• pp.445-450
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• 2011

We studied the adhesion characteristics of polymer films (PC, PET, EVA) treated by atmospheric pressure plasma. The process parameters were the frequency, gas flow, and treatment time; we studied the effects of these parameters on the adhesion characteristics of the polymer materials. We used de-ionized water and diiodomethane as the polar and nonpolar solvents, respectively, for measuring the contact angles, and subsequently calculated the surface free energy of each polymer film. The adhesion characteristics were studied by carrying out a $180^{\circ}$ peel-off test. The polymer films treated with plasma developed a hydrophilic surface, which led to increased surface free energy and improved adhesion properties. From the results for contact angle, surface free energy, and adhesion strength, we obtained the optimal plasma-treatment conditions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.10
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• pp.1202-1209
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• 2004

In this study, numerical investigation has been performed on the evolution of weld pool geometry with moving free surface during low-energy density laser welding process. The free surface elevates near the weld pool edge and descends at the center of the weld pool if d$\sigma$/dT is dominantly negative. It is shown that the predicted weld pool width and depth with moving free surface are a little greater than those with flat weld pool surface. It is also believed that the weld pool surface oscillation during the melting process augments convective heat transfer rate in the weld pool. The present analysis with moving free surface should be considered when We number is very small compared to 1.0 since the deformation of the weld pool surface is noticeable as We number decreases.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.133-138
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• 2003

In this study, numerical investigation has been performed on the evolution of weld pool geometry with moving free surface during low-energy density laser welding process. The free surface elevates near the weld pool edge if ${\partial}{\sigma}/dT$ is dominantly negative. On the contrary, the free surface rise at the center of weld pool in case of mainly positive ${\partial}{\sigma}/dT$. The predicted weld pool width and depth with moving free surface are 5∼15%$5{\sim}15%$ greater than those with flat weld pool surface. It is considered that weld pool surface oscillation during melting process augments convective heat transfer rate in the weld pool.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.1
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• pp.111-120
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• 1994

This is a continuing work of Van & Lee[1]. Some unresolved results of theirs are first discussed more, and then Tulis's[2] exact theory is briefly reviewed. A second order theory derived from Tulin's is used as a basis to judge the accuracy of the Poisson and the Dawson[3] free surface boundary condition(FSBC) in the low speed region for a two-dimensional submerged body. In search of a new FSBC, a purely numerical approach is adopted, and we show one candidate and its performance, which is satisfactory to a certain degree.

• Journal of the Society of Naval Architects of Korea
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• v.32 no.1
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• pp.58-69
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• 1995

The present paper is devoted to constructing a numerical algorithm for solving un steady problems on generation, propagation and interaction of nonlinear waves at a surface of ideal fluid, within the framework of the potential-flow model. The numerical scheme is implicit. with non-linearity iteration at every step of time. the finite-difference method with boundary-fitted coordinates are presented in favor for validity and high efficiency of the numerical model developed. Among these arguments, there are the results of calculations of two test problems-on stretching of a liquid ellipse and on wave generation by lifting a portion of a bottom.

• Journal of Ocean Engineering and Technology
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• v.4 no.1
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• pp.55-61
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• 1990

For the tracking of three dimensional free surface motions, a method referred to as the Volume of Fluid(VOF) algorithm is extended. In order to calculate the slope of three dimensional free surface which is the most important for the advection algorithm that decides the amount of fluid from cell to cell and for the application of free surface boundary condition, a simple method utilizing two dimensional slope informations is introduced. The extended algroithm is tested by demonstrating the simulation of a propagating sinusoidal wave through the channel whose width changes abruptly.

• Proceedings of KOSOMES biannual meeting
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• 2009.06a
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• pp.85-86
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• 2009

The sloshing phenomenon can be defined as the nonlinear movement of the free-surface of liquids inside tanks. It generates dynamic loads on the tank structure and thus becomes a problem of relative importance in the design of marine structures. The present study describes a experiment of the sloshing of flows with free-surface which contained in a rectangular tank moving in pitching motion.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.376-379
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• 2010

Bubble rising phenomenon is widely founded in many industrial applications such as a stream generator in power plant. Many experimental and numerical researches have been already performed to predict dynamic behavior of the bubble rising process. Recently numerical approaches are getting popular since it can offer much detailed information which is almost impossible to obtain from the experiments. Rising bubble could penetrate through the top free surface which makes the problem much more complicate in addition to the phase changing effect even with latest numerical techniques. In this paper, the top free surface effect on rising bubble has been investigated. The gas-liquid interface was explicitly tracked using high-order Level Contour Reconstruction Method(LCRM) which is a hybridization of Front-Tracking and Level-Set method. Break-up behavior of rising bubble at free surface showed different characteristics with initial diameter of bubble.